In order to set subtotals to display a blank cell rather than zero the following steps need to be taken:
1. In Strategy Developer execute a report, go to Data -> VLDB Properties ->Analytical Engine ->Null checking for Analytical
Engine.Uncheck "Use default inherited value - ( Default Settings)" and select "False" as shown below:

2. Save and Close the window. The grid cell will now display a blank cell instead of 0 for all subtotal values.